1. Field of the Invention
The present invention relates to a bearing unit for rotatably supporting a rotating shaft or rotatably supporting a rotating member to a shaft, motor using the bearing unit and electronic equipment using the motor.
2. Description of the Related Art
As a bearing unit for rotatably supporting a rotating shaft, the configuration shown in FIG. 9 is widely used (see Japanese Patent Laid-Open No. 2005-69382). Referring to FIG. 9, such a bearing unit 100 is generally shown. The bearing unit 100 has a rotating shaft 101, a radial bearing 102 for rotatably supporting the outer circumferential surface of the rotating shaft 101, a thrust bearing 103 for rotatably supporting the front end of the rotating shaft 101, a housing 104 for accommodating the radial bearing 102, and an oil seal 105 for preventing the leakage of a lubricating oil filled in the housing 104.
The housing 104 has a cylindrical shape having an open end from which the rotating shaft 101 is inserted and a closed end at which the thrust bearing 103 is provided. The radial bearing 102 is provided in the housing 104 at an intermediate portion between the open end and the closed end, and the oil seal 105 is provided at the open end of the housing 104.
The rotating shaft 101 is inserted through the radial bearing 102, and the lubricating oil is filled between the rotating shaft 101 and the radial bearing 102. Thus, the radial bearing 102 is provided by a hydrodynamic lubrication bearing having dynamic pressure generating grooves for generating a dynamic pressure by circulating the lubricating oil during rotation of the rotating shaft 101. The radial bearing 102 is formed of sintered metal containing copper or copper-iron as a main component, for example. The sintered metal has a porous structure as an inherent property, and this porous structure is utilized to hold the lubricating oil.
The outer circumferential surface of the radial bearing 102 is formed with a groove extending in the axial direction of the radial bearing 102. This groove provides a communication passage 106 defined between the outer circumferential surface of the radial bearing 102 and the inner circumferential surface of the housing 104. The communication passage 106 extends so as to make the communication between the closed end and the open end of the housing 104, thereby short-circuiting a dynamic pressure generated by the rotation of the rotating shaft 101. Accordingly, the expansion of air present in the housing 104 due to the generation of the dynamic pressure can be prevented to thereby prevent the scattering of the lubricating oil from the open end of the housing 104.
The oil seal 105 is mounted on an end surface at the open end of the housing 104 to prevent the leakage of the lubricating oil filled in the housing 104. The oil seal 105 is formed of metal or resin material, and it has an annular shape as having a shaft insertion hole 105a. The oil seal 105 is fitted to the open end of the housing 104 so as to come into abutment against an end surface of the radial bearing 102 exposed to the open end of the housing 104. Further, the rotating shaft 101 is inserted through the shaft insertion hole 105a of the oil seal 105 with a slight clearance defined therebetween. The surface of the oil seal 105 is treated by an oil repellent finish such that fluororesin is coated and baked, whereby a contact angle between the surface of the oil seal 105 and the lubricating oil filled in the housing 104 can be increased to thereby prevent the leakage of the lubricating oil. In the case that the oil seal 105 is formed of resin material, the mounted portion of the oil seal 105 to the housing 104 is sealed by welding such as thermal welding or ultrasonic welding.
In the bearing unit 100, a gap 110 is defined between the outer circumferential surface of the rotating shaft 101 and the inner circumferential surface of the oil seal 105 forming the shaft insertion hole 105a, and merely the gap 110 becomes a possible leak path of the lubricating oil filled in the housing 104. However, the width of the gap 110 is reduced to thereby utilize a surface tension of the lubricating oil exposed to the gap 110, thereby preventing the leakage of the lubricating oil from the gap 110 to the outside of the housing 104.
Further, the outer circumferential surface of the rotating shaft 101 opposed to the inner circumferential surface of the oil seal 105 forming the shaft insertion hole 105a is tapered toward the open end of the housing 104 as shown by reference numeral 101a. By the formation of the tapered portion 101a, a pressure gradient is formed in the gap 110 defined between the tapering outer circumferential surface of the rotating shaft 101 and the inner circumferential surface of the oil seal 105 forming the shaft insertion hole 105a. Accordingly, a force of drawing the lubricating oil from the gap 110 into the housing 104 is generated by a centrifugal force generated by the rotation of the rotating shaft 101. Thus, during rotation of the rotating shaft 101, the lubricating oil is drawn into the housing 104, so that the lubricating oil can be reliably supplied to the dynamic pressure generating grooves formed on the radial bearing 102 as a hydrodynamic lubrication bearing to thereby realize stable bearing of the rotating shaft 101 during rotation and to also prevent the leakage of the lubricating oil filled in the housing 104.